In accordance with a rapid spread of information relevant apparatuses and communication apparatuses such as a personal computer, a video camera and a portable telephone in recent years, the development of a battery to be utilized as a power source thereof has been emphasized. The development of a high-output and high-capacity battery for an electric automobile or a hybrid automobile has been advanced also in the automobile industry. A lithium battery has presently drawn attention from the viewpoint of a high energy density among various kinds of batteries.
In the field of lithium batteries, conventionally, the interface of electrode active materials has been focused and the attempts to improve the performance of lithium batteries have been made; for example, a technique to coat an active material with a Li-containing compound has been considered. Patent Literature 1 discloses a technique to form a reaction suppressing part comprising, for example, a polyanion structure containing compound (such as Li3PO4—Li4SiO4) in a cathode active material that contains a transition metal (such as LiCoO2), using a sol-gel method. Also, Patent Literature 2 discloses a method for producing a lithium cathode active material comprising a coating part including a Li element, a P element, and Mn derived from a P element and a cathode active material on a surface of an oxide cathode active material including Mn, wherein in an interface of the cathode active material and the coating part, Mn/P is 1 or more; and the coating part is formed by a sputtering method using Li3PO4 as a coating material.